The study showing calretinin (CR) mRNA localization in the reticular formation (RF) of the rat and CR immunoreactive cells coexpressing glutamate receptors has been completed and submitted for publication. A study examining the interaction of CNS drugs and sensory stimulation on calcium binding proteins and other cellular markers continues. Rats treated with morphine (10 mg/kg) failed to habituate to the behavioral arousing effects of intermittent tone presentations. A marker of immediate early gene activation (p-CREB immunoreactivity) revealed unique patterns of neuronal staining in the RF of animals exposed to tones and morphine. Examination of cfos mRNA revealed a morphine induced decrease in the piriform cortex which was unaffected by tone stimulation and an increase in cfos mRNA in the cochlear N. of rats exposed to tones, regardless of morphine treatment. No changes in PV or CR mRNA have been observed (cochlear N. or RF). A comparative study revealed a population of cells of the anteroventral cochlear nucleus (AVCN) that express CR in guinea pigs but not rats. Parvalbumin mRNA was detected in AVCN cells of both species. These results suggest a common calcium buffering function of these proteins in subpopulations of auditory cells. A study of the developmental expression of CR in the chick equivalent of the cochlear nucleus is nearly completed. Results indicate that CR expression is not uniquely associated with the establishment of neuronal activity. Removal of otocysts (primordium of the inner ear) of chicks did not influence the developmental expression of CR mRNA in the auditory brainstem. Conductive hearing loss produced by columella removal at early post hatching days (P1-7), also did not affect CR expression. However, columella removal in older animals may decrease CR mRNA. These data indicate that neuronal activity may play a greater role in regulating CR expression in mature than in the developing chick auditory system.